Date:   Mon, 12 Jun 2017 15:22:44 +0200
From:   Mason <slash.tmp@...e.fr>
To:     netdev <netdev@...r.kernel.org>
Cc:     Florian Fainelli <f.fainelli@...il.com>,
        Andrew Lunn <andrew@...n.ch>, Mans Rullgard <mans@...sr.com>,
        Thibaud Cornic <thibaud_cornic@...madesigns.com>
Subject: Toggling link state breaks network connectivity

Hello,

I am using the following drivers for Ethernet connectivity.
drivers/net/ethernet/aurora/nb8800.c
drivers/net/phy/at803x.c

Pulling the cable and plugging it back works as expected.
(I can ping both before and after.)

However, if I toggle the link state in software (using ip link set),
the board loses network connectivity.

# Statically assign IP address
ip addr add 172.27.64.77/18 brd 172.27.127.255 dev eth0
# Set link state to "up"
ip link set eth0 up
# ping -c 3 172.27.64.1 > /tmp/v1

PING 172.27.64.1 (172.27.64.1): 56 data bytes
64 bytes from 172.27.64.1: seq=0 ttl=64 time=18.321 ms

--- 172.27.64.1 ping statistics ---
3 packets transmitted, 1 packets received, 66% packet loss
round-trip min/avg/max = 18.321/18.321/18.321 ms


172.27.64.1 is a desktop system.
Running
% tcpdump -n -i eth1-boards ether host 00:16:e8:4d:7f:c4
on the desktop, I get:

15:01:45.187346 ARP, Request who-has 172.27.64.1 tell 172.27.64.77, length 46
15:01:45.187359 ARP, Reply 172.27.64.1 is-at 00:15:17:24:e0:81, length 28
15:01:45.194633 IP 172.27.64.77 > 172.27.64.1: ICMP echo request, id 41219, seq 0, length 64
15:01:45.194662 IP 172.27.64.1 > 172.27.64.77: ICMP echo reply, id 41219, seq 0, length 64
15:01:50.198564 ARP, Request who-has 172.27.64.77 tell 172.27.64.1, length 28
15:01:50.205929 IP 172.27.64.77 > 172.27.64.1: ICMP echo request, id 41219, seq 1, length 64
15:01:50.205951 IP 172.27.64.1 > 172.27.64.77: ICMP echo reply, id 41219, seq 1, length 64
15:01:50.213217 IP 172.27.64.77 > 172.27.64.1: ICMP echo request, id 41219, seq 2, length 64
15:01:50.213232 IP 172.27.64.1 > 172.27.64.77: ICMP echo reply, id 41219, seq 2, length 64
15:01:51.198563 ARP, Request who-has 172.27.64.77 tell 172.27.64.1, length 28
15:01:51.209586 ARP, Reply 172.27.64.77 is-at 00:16:e8:4d:7f:c4, length 46
15:01:51.209598 ARP, Reply 172.27.64.77 is-at 00:16:e8:4d:7f:c4, length 46

Packet #1: the board asks for the desktop's MAC address
Packet #2: the desktop replies instantly
Packet #3: the board sends the first ping
Packet #4: the desktop replies instantly
Then the board goes quiet for a long time (why???)
Packet #5: the desktop asks for the board's MAC address (doesn't it have it already?)
Packet #6: this seems to unwedge the board, which sends the second ping
Packet #7: the desktop replies instantly
Packet #8: the board sends the third ping
Packet #9: the desktop replies instantly
Packet #10: the desktop asks again for the board's MAC address
Packet #11 and #12: the board answers twice (for the old and new requests?)

Some oddities, but it seems to work.

Now toggle the link state:

% ip link set eth0 down
% ip link set eth0 up
% ping -c 3 172.27.64.1 > /tmp/v2

PING 172.27.64.1 (172.27.64.1): 56 data bytes

--- 172.27.64.1 ping statistics ---
3 packets transmitted, 0 packets received, 100% packet loss


On the desktop, I see

15:14:03.900162 ARP, Request who-has 172.27.64.1 tell 172.27.64.77, length 46
15:14:03.900175 ARP, Reply 172.27.64.1 is-at 00:15:17:24:e0:81, length 28
15:14:05.017189 ARP, Request who-has 172.27.64.1 tell 172.27.64.77, length 46
15:14:05.017200 ARP, Reply 172.27.64.1 is-at 00:15:17:24:e0:81, length 28
15:14:06.030531 ARP, Request who-has 172.27.64.1 tell 172.27.64.77, length 46
15:14:06.030541 ARP, Reply 172.27.64.1 is-at 00:15:17:24:e0:81, length 28

So basically, the board is asking the desktop for its MAC address,
and the desktop is answering immediately. But the board doesn't seem
to be getting the replies... Any ideas, or words of wisdom, as they say?

Regards.

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